In spite of several decades of intensive study, many prominent features of the physiology of visual cortex have not been fully elucidated. Among these are 1) the precise mapping of different retinal ganglion cell classes onto the diversity of cortical areas, layers and cell types, and 2) the mechanisms by which retinal signals are converge onto cortical cells so as to produce emergent properties such as orientation selectivity. In this proposal, we present a new method which permits direct exploration of these and other issues. We plan to record simultaneously from cortical cells and retinal ganglion cells with overlapping receptive fields, and by means of cross-correlating their spike trains, to identify the specific retinal inputs to cortical cells. By systematically mapping multiple retinal inputs to single cortical cells, we can test hypotheses about the contributions that these inputs make to cortical cell receptive field structure and properties. We can also compare the spatial and temporal tuning characteristics of cortical cells with that of their inputs, and can identify the contributions that X, Y, and W cells make to the functional attributes of cortical areas 17, 18, and 19 and their constituent cell types. These results will greatly expand our understanding of information processing in the visual system, and will establish a foundation upon which to understand the functions of intrinsic cortical circuits.